1. Field of the Invention
The present invention generally relates to methods of registering the locations of mobile communication systems, and, more particularly, to a method of registering the location in a mobile communication system that registers the location of each mobile device. The present invention also relates to the mobile device.
2. Description of the Related Art
A mobile communication system comprises a plurality of base stations, and a mobile device connected to a mobile switching center via the base stations, thereby establishing a connection with another mobile device or a fixed device. To call a mobile device, the mobile switching center needs to grasp where the mobile device is located, i.e., near which base station the mobile device is located.
Conventionally, a location area (or a network fixed location registration area) LAi is allocated to each group of base stations, as shown in FIG. 1. In this figure, each small circle represents the area of a base station, and each large circle represents a location area. In this case, only when a mobile device moves from one location area to another, the mobile device transmits a location registration signal to the mobile switching center, thereby performing a location registration operation. The mobile switching center manages the location of the mobile device in each location area LAi. When the mobile device receives a call, a simultaneous call operation is performed on all the base stations corresponding to the location area LAi in which the location of the mobile device is registered.
The information of each location area LAi is incorporated in notification information that is constantly sent from the base stations. The mobile device compares its location area LAi with the location area LAi defined by the notification information. If the location area LAi of the mobile device does not coincide with the location area LAi, the mobile device transmits a location registration signal so as to perform a location registration operation. The mobile switching center manages the information of each mobile device, including the current location (i.e., the location area LAi). The information is managed by a HLR (Home Location Register) or a VLR (Visitor Location Register). When the mobile device receives a call, the mobile switching center refers to the HLR or VLR, and reads out the location area LAi corresponding to the mobile device. All the base stations (BSj) corresponding to the location area LAi then simultaneously call the mobile device.
If each location area LAi is made smaller, the call signal traffic can be made smaller accordingly, but the location registration signal traffic is increased. If each location area LAi is made larger, the location registration signal traffic can be made smaller, but the call signal traffic is increased. Therefore, in a mobile communication network, the size of each location area LAi (or the number of base stations) is determined in such a manner as to optimize the balance between the location registration signal traffic and the call signal traffic.
To reduce the location registration signal traffic and the call signal traffic, various suggestions have been made. In a case where a mobile device moves in the vicinity of the boundary of a location area LAi, to prevent an increase in location registration signal traffic, the location area has a hierarchical structure. More specifically, a first-layer location area and a second-layer location area have different boundaries from each other. If the location of a mobile device changes in the first-layer location area LAi, the location is registered in the second-layer location area, thereby giving hysteresis to the location registration operation.
For a mobile device having a high motion frequency and a small call reception frequency, a location registration operation is performed with a location area LAi that extends in a wide area. On the other hand, for a mobile device having a low motion frequency and a high call reception frequency, a location registration operation is performed with a location area LAi that extends only in a narrow area, thereby reducing the location registration signal traffic and the call signal traffic. However, those location areas LAi are selected from predetermined ones on the network side, resulting in unnecessary call signal traffic.
Generally, a person""s sphere of action is limited. For some people, a location registration operation is performed between their houses and workplaces. For others, a location registration operation is performed only in the vicinity of their houses. In this case, the location registration operation in the location registration area shown in FIG. 1 results in unnecessarily large call signal traffic. In order to avoid such unnecessary call signal traffic, the following suggestions have been made.
Japanese Laid-Open Patent Application No. 8-84364 discloses a mobile switching center call system in a cellular phone network. As shown in FIG. 2, in a case where a mobile device frequently moves between two location registration areas MLA1 and MLA2, it is necessary to restrict the location registration signal traffic that increases every time the location registration areas are changed. In the mobile switching center call system, the following operation is performed. A plurality of base stations near which the mobile device has a high probability of being located are determined in advance, in accordance with the tendency of call transmission and reception of the mobile device. The plurality of base stations are then registered as a virtual mobile location area VMLA that is inherent to the mobile device, thereby preventing a location registration operation even when the mobile device moves within the location registration areas MLA1 or MLA2. The base stations in the virtual mobile location area VMLA are a first call group, the base stations in the rest of the location registration area MLA1 are a second call group, and the base stations in the rest of the location registration area MLA2 are a third call group. When the mobile device receives a call, the first call group, the second call group, and the third call group are called in this order.
Japanese Laid-Open Patent Application No. 9-116952 discloses a mobile communication system in which a location registration area is formed within each user""s sphere of action, as shown in FIG. 3. When the mobile device is located within the location registration area, a location registration operation is not performed, thereby reducing the location registration signal traffic. The mobile device counts the number of base stations near which the mobile device passes, and notifies the network of the result, if necessary. The mobile device notifies the mobile switching center of which base stations the mobile device frequently passes near and stays over a long period of time.
The mobile switching center stores the base stations notified from the mobile device. When the mobile device receives a call, the mobile switching center carries out a simultaneous call operation on all the registered base stations for the mobile device. Also, depending on the passing count number and the duration of stay, the base stations are grouped in the descending order of probability of having the mobile device staying therein. In FIG. 3, the staying probability of the mobile device is the highest at the base stations with black solid circles, the second highest at the base stations with double circles, and the lowest at the base stations with single circles. When the mobile device receives a call, the mobile switching center first calls the base stations with the black solid circles. If the mobile switching center cannot detect the mobile device, the mobile switching center calls the base stations with the double circles for the mobile device. If the mobile device cannot be found yet, the mobile switching center calls the group of base stations with the single circles. If the mobile device moves outside the shaded area, which represents the location registration area of the mobile device in FIG. 3, the mobile device can detect the base station ID notified from the base station. Accordingly, the mobile device can compare the notified base station ID with base station IDs stored in the mobile device (represented by the shaded areas). By doing so, the mobile device recognizes that the mobile device has moved out of its own location registration area, and then registers the normal location registration area as shown in FIG. 1.
Japanese Laid-Open Patent Application No. 10-303530 discloses a mobile communication system in which each mobile terminal manages the location detection history, and base stations at which base station switching often occurs are grouped into personal location registration areas in accordance with the motion characteristics of each terminal, as shown in FIG. 4. In this system, the location registration signal traffic and the call signal traffic are reduced.
Japanese Laid-Open Patent Application No. 5-336026 discloses a mobile communication system in which a location registration area into which a mobile device enters next is estimated from the moving direction and the moving speed of the mobile device. In this system, a location registration operation is performed in a location registration zone that is long in the moving direction and short in the direction vertical to the moving direction, so that the location registration signal traffic and the call signal traffic are reduced.
In the system disclosed in Japanese Laid-Open Patent Application No. 8-84364, however, when the motion range becomes too wide, or the location registration area becomes too wide with microcells, the paging signal traffic is increased with a large virtual mobile location area VMLA. Also, with a small virtual mobile location area VMLA, the probability that the mobile device can be called in the small virtual mobile location area VMLA becomes low. Furthermore, the sequential call operation might take time to reach the mobile device, resulting in large signal traffic.
In the system disclosed in Japanese Laid-Open Patent Application No. 9-116952, the base stations in the location registration area of a mobile device are called in the descending order of probability of having the mobile device therein. This system is effective as long as there is a large difference in the probabilities. However, if all the base stations has similar probabilities, this system does not work very effectively. Also, if the mobile device is located at the base station to be called last, it takes a long time until the mobile device actually receives a call. In such a case, the call signal traffic also increases.
In the system disclosed in Japanese Laid-Open Patent Application No. 10-303530, a location registration area is formed for each user, and the location registration signal traffic and the call signal traffic can be reduced. However, when the mobile device is stationary, a location registration operation is performed on a plurality of base stations. As a result, the plurality of base stations are called when the mobile device is to receive a call. This calling signal traffic can be reduced by reducing the number of base stations registered in the stationary state. For instance, the call signal traffic can be reduced to a third by reducing the number of base stations to one. This means that this system has the problem of unnecessarily traffic.
In the technique disclosed in Japanese Laid-Open Patent Application No. 5-336026, each mobile device needs to have a function of detecting the motion speed and direction. If no detectors for detecting the motion speed and direction are provided, the motion speed and direction can be calculated from the coordinates of the latest base station that has received a call. However, the motion speed and direction cannot be very accurately determined in this system. Therefore, it is necessary to mount a detector for detecting the motion speed and direction on the mobile device, resulting in high costs.
A general object of the present invention is to provide methods of registering locations in a mobile communication system and mobile devices in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a method of registering a location in a mobile communication system and a mobile device used in the system that can reduce a call signal traffic without increasing the location registration signal traffic.
The above objects of the present invention are achieved by a method of registering a location in a mobile communication system in which one or a plurality of base stations are connected to a mobile switching center that manages a location of a mobile device in accordance with a location registration from the mobile device, and in which a simultaneous call connection is performed on the registered one or plurality of base stations when the mobile device receives a call. This method comprises the steps of:
transmitting a base station ID for identifying each base station from each corresponding base station, the base station ID being incorporated into notification information;
storing the base station ID as a history of the mobile device when the base station ID indicated by the notification information changes, or when a predetermined period of time has passed;
statistically predicting one or a plurality of base stations near which the mobile device will pass by next, in accordance with the latest history of the mobile device;
registering the predicted one or plurality of base stations as a personal location registration area; and
extracting the registered personal location registration area based on the history of the mobile device, thereby performing a location registration operation.
By this method, a location registration operation can be performed with the optimum personal location registration area for each mobile device. Thus, the call signal traffic can be further reduced without increasing the location registration signal traffic.
The above objects of the present invention are also achieved by a mobile device in which one or a plurality of base stations are connected to a mobile switching center that manages a location of the mobile device in accordance with a location registration from the mobile device, and in which a simultaneous call connection on the registered one or plurality of base stations is carried out when the mobile device receives a call. This mobile device comprises:
a base station ID detection unit that detects a base station ID that identifies each base station, the base station ID being incorporated in notification information supplied from each corresponding base station;
a reception base station ID storage unit that stores the base station ID as a history of the mobile device, when the base station ID indicated by the notification information changes, or when a predetermined period of time has passed;
a predicted location registration unit that statistically predicts one or a plurality of base stations near which the mobile device will pass by next, in accordance with a latest history of the mobile device stored in the reception base station ID storage unit, and registers the predicted one or plurality of base stations as a personal location registration area; and
a location registration unit that extracts the personal location registration area registered in the predicted location registration unit, base on the history of the mobile device stored in the reception base station ID storage unit.
With this mobile device, a location registration operation can be performed with the optimum personal location registration area for each mobile device. Thus, the call signal traffic can be further reduced without increasing the location registration signal traffic.